Method of concentrating diolefins



`Aug. '7, 1945. R. F. ROBEY ET Al. l

METHOD OF CONCENTRATlNG DIOLEFINS Filed Sept. 6, 1941 ons wo o m6 $6 QN 1mm. OM, WM, Q lav Ohh. 19h. QW O W m S A UOO wwvk S505 OOM wkouuow Nkwkqbm. WDONKJU a wnl MINNAOQ &%m ko 3 ZORNOWNQ 2Q "l lo Lvhkkw \.Q `n gl w 1 ,No s v, m m6 n 1 o v\ fl 1 $-Q W 1 1 f \&\ s l..

Patented 7, 1945` l i 2,381,311 Y METHOD oF CONCENTRATING DIoLErTNs l Rich/ard F. Robey, Roselle, and Miller W. Swaney, Linden, N. J., assignors, by mesne assignments,

to Jasco, ,"Louisiana Incorporated, a corporation of Application September 6, 1941, Serial No. 409,778

' s' claims. (ci. 26o-681.5)

Thisy invention relates to the separation and concentration of dioleilns from gaseous mixtures containing oleiins, diolens, saturated hydrocarbons, and other gases, and relates particularly to the separation and concentration of diolens, both gaseous and liquid, from `mixtures of unsaturated and saturatedhydrocarbons using improved types of cuprous salt solutions.

Rarely are pure hydrocarbons produced in inindustrial processes, particularly in cracking processes. For example, C4 cuts from petroleum refinery operations consist mainly of normal and isobutane, isobutene and the normal butenes-l and 2, and, in addition, butadiene-1,3.` This diolefln, which is a. desirable raw material for polymerization reactions, such as in the production of synthetic rubber, possesses a boiling point (-4.5 C.) which lies close to, and between', the boiling points of the other C4 hydrocarbons. Therefore, the separation of pure butadiene from composite C4 cuts by physical manipulations such as distillation, et'c., is impractical. The separation, in a pure state, if isoprene and piperylene from composite C5 cutsis equally diflicult.

The separation of some of the lower olens, such as ethylene and propylene, from saturated hydrocarbons has been accomplished by means of selective absorption in cuprous salt solutions (acidic, neutral or basic), an example of this being the separation of ethylene from ethane by contacting with ammoniacal cuprous chloride solutions (in which the olefin is the more soluble), followed by regeneration of high purity ethylene by heating.

Inaddition to ammoniacal cuprous salt solutions, other amine-copper complexes have found use in separating mono-olen's from parafflns. Among these are the hydroxylated alkylamines .(e. g., monoethanolamine, eta). Ethylene and propylene have been separated from their sat-` urates by means of pyridine solutions of certain copper salts, such as pyridine cuprous acetate solutions (U. S. Serial No. 248,471, led December 30, 1938, by R. F. Robey, now Patent 2,245,719.

In the `further separation of dioleiinic hydrocarbons from the mono-olefins, thev range of ap.

plicablity of cuprous salt solutions is much more limited. For instance, the ammoniacal cuprous salt solutions such as cuprous ammonium chloride, acetate, sulfate, etc., arevery elective for the separation of butadiene from mixtures with the various butenes. yAs an illustration, certain ammoniacal cuprous acetate solutions (3 4 normal Cu+) may absorb up to 25-30 volumes of` ethanolamine-cuprous salt complexes. Yet, when applied to the extraction of isoprene or piperylene from mixtures with pentenes, these solutions are almost completely ineffective. For example, the ammoniacal cuprous acetate solution which absorbsup to 25-30 volumes of pure butadiene gas, dissolves only 1-2 volumes of isoprene gas under similar circumstances.

Of a considerable number of organic 'aminecopper complexes investigated, only one class proved effective for the extraction of the diole- I fins higher than butadiene, namely, cuprous, salt complexes solubilized with pyridine, a heterocyclic organic base.

An object of this invention is to provide a solution that may be usedfor the separation and 'concentration of the diolens in a substantially K ing combination of this class is the pyridineand piperylene.

cuprous sulfate complex which possesses not only a high absorption capacity for C5 dioleiins but, as We1l,exhibits a very high selectivity for-isoprene As the later examples illustrate, when a pyridine-cuprous sulfate solution of only 2.0 normal copper content is contacted with a C5 blend containing only 20% of isoprene, the copper solution on subsequent desorption yields an isoprene product of 98% purity. Such a solution dissolves 1 15-16 volumes (measured as S. T. P.) of pure isoprene gas or 13-14 volumes of pure piperylene. Whereas the cuprous ions engaged in the cuprous salt-ammonia complexes do not possess suflicient activity to combine with dioleflns higher than butadiene, the copper in active amine-copper complexes, but also other bases of the pyridine series are of importance. For example, the picolines (alpha, beta, and gamma-methyl-pyridines) form very stable and desirable complexes with cuprous salts.

Although several of the pyridine-cuprous sulpure butadiene gas. This is likewise true of the fate complexes possess definite merit as extractants for the Cs dioleiins, the optimum diolen absorbing solutions as proposed by the present inventionlare those of the pyridine cuprous sulfate class o1' .about 2.0 normal cuprous ion content, and possessing pH values in the range of 4 as illustrated by Example IV.

The pyridine cuprous sulfate solutions are prepared by adding cuprous oxide t`aqueous solutions of pyridine andI pyridine sulfate, in the absence of air. The 'completely cuprous solutions are of clear light-amber color, which turns to bright green when a small proportion of thetotal copper present becomes oxidized to the cupric state. An optimum solution is prepared by mixing 127 parts by weight of pyridine, 35 parts of cuprous oxide (Cu-10) 100 parts of water and 48 parts of 94% H2804. A clear solution results almost immediately which is 2.0 normal in cuprous content and of 4.0 pH.

The pyridine-cuprous acetate, lactate, and sulfate solutions were found to possess the unexpected and extremely important advantage of being stable in contact, with available metals of construction in spite of the fact that some of these solutions'are quite acidic in nature. For example, pyridine-cuprous sulfate solutions of 4.0 pH or lower are completely stable in contact with copper or stainless steel at 90l00 C. for indefinite periods.

The following examples serve to illustrate the presentinvention:

EXAMPLE .I

diene, it was found to dissolve nearly 30 volumesl of Cil-ic per volume of solution. This signifies that about (S5-70% of the total cuprous ions present had combined in absorbing butadiene.

(b) When the ammoniacal copper solution (described in p art a) was-saturated at 5 C. with a C5 blend comprising 25% isoprene and 75% trimethylethylene (2 methylbutene 2) and the phases separated, the copper solution, upon desorption, yielded only 1.6 volumes of isoprene of only 78% purity. In this instance, the cuprous ions in this complex solution were of such low activity that practically none had combined with isoprene. The small amount of isoprene actually dissolved would account for only 3% utilization of Cu+, excluding physically dissolved isoprene.

When this extraction was repated using a 25% piperylene blend an even smaller amount of dioleiin was dissolved which corresponded to only.

2% Cu+ utilization.

EXAMPLE II (a) An aqueous pyridine-cuprous acetate solution of 1.8 normal copper content was prepared by dissolving cuprous oxide in a pyridine-acetate solution until saturated with copper. When the solution thus prepared was brought to equilibrium with pure gaseous butadiene at C., 22.5 volumes of butadiene were dissolved by each volume of copper solution, denoting substantially av 100% utilization of Cu+ in forming the Cu2++buta diene complex.

(b) When a pyridine-cuprous lactate solution of 1.8 normal Cu+ 'content was contacted at 0 C. with a low purity isoprene blend (25% in trimethly-ethylene) it was found to dissolve more than 7 volumes of isoprene gas per volume of copper solution used.

EXAMPLE III (a) -A pyridine-cuprous sulfate solution of 2.0 normal Cut content, and prepared as described above was contacted at +10 C. with pure gaseous butadiene whereupon 21 volumes of butadiene were dissolved per volume of solution employed. This represents a utilization of substantially of the total cuprous ions in this highly active complex in uniting with butadiene.

When this solution was further contacted with low purity butadiene under similar circumstances, this dioletin was concentrated from 20% to over 92% in a single extraction step.

(b) Even though an ammoniacal copper complex solution almost twice as concentrated in cuprous ions failed to appreciably dissolve isoprene or piperylene, as illustrated in Example I, the 2.0 normal pyridine-cuprous sulf'ate solution (described in part a), when contacted with pure liquid isoprene at 0 C., dissolved 16-17 volumes of this Cs diolefin per volume of solution, representing a Cu+ utilization of about 75%. In a separate test the absorption efficiency for piperylene was found to be almost as high.

(c) When this pyridine-cuprous sulfate solution was contacted at 0 C. with low purity isoprene (25% in trixnethylethylene) and subsequently desorbed it yielded over 11 volumes of gaseous isoprene of 92-94% purity and suitable for use directly in many reactions. When the saturated pyridine-cuprous sulfate solution was desorbed in two stages, so as to flash off. traces of pentenes in the iirst step, an isoprene product of 98% purity was produced.

EXAIVIPLE IV Eect of solution pH on solubility of 25% isomene-75% trmethylethylene in pyridine cuprous sulfate solutions (liquid phase extractions, 0 C.)

So1u Vols. Cs -Percent Vols. ure tion Cu+ norabsorbed isoprene 05H! vol Mols 05H11/ pH mality per vol. in prod- Cu solu mol Cuz++ Cu soin. uct (S. T. P

The. above examples illustrate the merits of the present invention and the excellent superiority of the pyridine-cuprous salt complexes as extractants for dioletlns, both gaseous and liquid. Although, all -the examples presented herein involved regeneration of diolefins from copper solutions by, means of heat, this may also be accomplished by subjecting the copper solution to reduced pressures, or by contacting it with a hydrocarbon boiling above or below the diolen being concentrated, or by stripping with an inert gas. These examples arel not intended. as a limitation but for illustration only.

We claim:

.1. A process for the separation of a diolen from a hydrocarbon mixture by means of a, se-

lective extraction with a solution comprising a cuprous salt dissolved in a. pyridine base.

2. A process for the production of a diolen of high purity which comprises contacting a hydrocarbon mixture containing a, diolefln, mono-olens; and saturates with a solution of a. cuprous salt dissolved in a pyridine base, separating the copper salt phase and heating to regenerate the desired diolen of high purity.

3. A -proces for the production of dioleilns of high purity which comprises contacting hydrocarbon mixtures containing the desired dioleiins with' an laqueous solution of a cuprous salt dissolved in pyridine, separating the pyridine-cuprous salt solution and heating to regenerate the diolens of high purity.

4. A process for the production of diolens of high .purity` which comprises contacting hydrocarbon mixtures containing these diolens with pyridine-cuprous salt solutions of about 2.0 normal cuprous ion content at a temperature of 0 C., separating said cuprous salt solution and heating to about -80 C. to regenerate the diolens of high purity. l

5. A process according to claim 4 in which the cuprous salt is the acetate.

6. A process for the production of diolens of high purity which comprises contacting mixtures of the diolens with other hydrocarbons with aqueous pyridine-cuprous sulfate solutions at temperatures of about -10 to +10 C., separating the solution therefrom and heating to about 70-80 C. to regenerate the desired diolens of high' purity.

7. A process -for the production of isoprene of high purity which comprises contacting mixtures of isoprene and pentenes and pentanes at about 0 C. with an aqueous pyridine-cuprous sulfate solution of aibout 2.0 normal cuprous content and of about 4.0 pH, separating the cuprous solution therefrom and heating to regenerate the desired isoprene of 100% purity.

8. A process according to claim 7 in which the desired diolens consist of a mixture of isoprene and piperylene. l

RICHARD F. ROBEY.

MILLER W. SWANEY. 

